Request.UrlReferrer is null after file download

I have developed an ASP site. I have a function to check the session's validity. I check whether the ReferrerURL is null and redirect to a session expired page if it is null. It works fine for all pages.

But after a file download ( using the response.TransmitFile ) when i refresh the page the ReferrerURL is null which results in the "Session Expired" redirection.

I have developed an ASP site. I have a function to check the session's validity. I check whether the ReferrerURL is null and redirect to a session expired page if it is null. It works fine for all pages.
But after a file download ( using the response.TransmitFile ) when i refresh the page the ReferrerURL is null which results in the "Session Expired" redirection.

Since you did provide any code relating to the Request.UrlReferrer is null